On Sun, Jul 24, 2016 at 11:33 AM, Gleb Natapov <g...@scylladb.com> wrote:
> On Sun, Jul 24, 2016 at 11:27:02AM +0200, Benoît Canet wrote: > > ZFS is also used on ubuntu. > > > So what? It does not changes the fact that writing using write() system > call does not go through out write page cache on OSv. It does go through > Linux' page cache on Linux. > > > > What make me think about page cache is the fact that ubuntu issue minimal > > write of 4K. > On Linux every write (if not O_DIRECT) goes through the page cache. > > > > > They store their data on an NFS server. > You mean VM's disk is on NFS server and they enables cache = none? > Otherwise tcpdump is meaningless. > yes. My pocket theory it that linux page cache will coalesce some small write hence giving it an advantage. > > > > > Best regards > > > > Benoît > > > > On Sun, Jul 24, 2016 at 11:25 AM, Gleb Natapov <g...@scylladb.com> > wrote: > > > > > On Sun, Jul 24, 2016 at 11:14:49AM +0200, Benoît Canet wrote: > > > > Hi, > > > > > > > > I am working on a slowness bug affecting the EU project. > > > > > > > > In this test HDFS a java application does a write test 7 times slower > > > than > > > > Linux. > > > > > > > > The people doing the test sent me some tcpdump traces and it show > that > > > OSv > > > > is doing > > > > small 1 sectors writes while Linux is doing at minima 4KB write. > > > > > > > > So I am starting to suspect that this slowness is due to the fact > that > > > OSv > > > > does not have a page > > > > cache enabled that could coalesce the writes. > > > > > > > > Gleb: Should the write page cache be different from arc ? Or should > we > > > rely > > > > on ARC for this ? > > > > > > > Why do you think page cache is involved at all? How do they write? The > > > program you implemented last time to demonstrate the problem does not > > > use our write cache at all. > > > > > > The fact that they use tcpdump to track their writes make me believe > > > that they do not use XFS and our page cache works only with XFS, > > > anything else does not have any page cache at all. > > > > > > -- > > > Gleb. > > > > > -- > Gleb. > -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to osv-dev+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
